<template>
	<ul class="list">
		<li 
			class="item" 
			v-for="item of letters" 
			:key="item"
			:ref="item"
			@click="handleLetterClick"
			@touchstart="handleTouchstart"
			@touchmove="handleTouchMove"
			@touchend="handleTouchEnd"
		>
			{{ item }}
		</li>
	</ul>
</template>

<script>
	export default {
		name: 'CityAlphabet',
		props: {
			cities: Object
		},
		computed: {
			letters() {
				const letters = []
				for (let i in this.cities) {
					letters.push(i)
				}
				return letters
			}
		},
		data () {
			return {
				touchStatus :false,
				startY: 0,
				timer: null
			}
		},
		updated () {
			this.startY = this.$refs['A'][0].offsetTop
		},
		methods:{
			handleLetterClick : function (e) {
				this.$emit('change',e.target.innerText)
			},
			handleTouchstart : function () {
				this.touchStatus = true
			},
			handleTouchMove : function (e) {
				if (this.touchStatus) {
					if(this.timer){
						clearTimeout(this.timer)
					}
					this.timer = setTimeout(() => {
						const touchY = e.touches[0].clientY - 79
						const index = Math.floor((touchY - this.startY) / 20)
						if(index >= 0 && index <this.letters.length){
							this.$emit('change',this.letters[index])
						}
					},16)
				}
			},
			handleTouchEnd : function () {
				this.touchStatus = false
			}
		}
	}
</script>

<style lang="stylus" scoped>
	@import '~styles/varibles.styl'
	.list
		display:flex
		flex-direction:column
		justify-content:center
		position:absolute
		right:0
		top:1.58rem
		bottom:0
		width:.4rem
		.item
			text-align:center
			line-height:.4rem
			color:$bgColor
</style>